FR2494533A1 - METHOD AND APPARATUS FOR RECORDING / RENDERING A CONTROL SIGNAL IN A VCR - Google Patents

Abstract

THE VCR ACCORDING TO THE PRESENT INVENTION INCLUDES AT LEAST ONE ROTATING MAGNETIC HEAD HV FOR RECORDING AND RETURNING A VIDEO SIGNAL ON AND FROM A MAGNETIC RECORDING TAPE T AND A FIXED HEAD HCA USED TO RECORD A CONTROL SIGNAL FOR WHICH IS INTENDED CONTROL THE ROTATION OF THE HV ROTATING HEAD AND THE MOVEMENT OF THE T-BAND. THE GAP OF THE HCA FIXED HEAD EXTENDS IN THE CROSS DIRECTION OF THE T-BAND SO AS TO COVER ALL OR ALMOST ALL OF THE WIDTH OF THE T-BAND. T-BAND THE CONTROL SIGNAL IS THEREFORE RECORDED ON THE MAGNETIC T-BAND OVER ALL OR ALMOST ALL OF THE WIDTH OF IT, WHICH PREVENTS AN UNWANTED DISAPPEARANCE OF THIS SIGNAL. BY SUPPLYING THE HCA FIXED HEAD WITH A HIGH FREQUENCY DELETE CURRENT IN CONJUNCTION WITH THE CONTROL SIGNAL, THE FIXED HEAD CAN OPERATE NOT ONLY AS A CONTROL SIGNAL RECORDING HEAD BUT ALSO AS A DELETE HEAD. A HEAD OF THE DOUBLE INTERFACE TYPE SHOWING A HIGH ERASING EFFICIENCY CAN BE USED IF THE DISTANCE BETWEEN THE TWO GAPS ARE GIVEN A CERTAIN VALUE OR IF THE TWO GAPS ARE GIVEN DIFFERENT WIDTHS.

Description

Method and apparatus for recording-restoring a control signal in

  The present invention relates, in general, to a method and an apparatus for recording and playback.

  tion of a control signal on and from a tape

  magnetic registration for use with a magnetic

  toscope comprising at least one rotating head.

  In a VCR with at least one rotating magnetic head of the helical scanning type, a fixed magnetic head is used to record and output a control signal to and from a magnetic recording tape. The control signal is recorded by the fixed magnetic head along the direction of movement of the strip on an edge thereof before recording a signal

  video. The control signal recorded on the tape remains

  killed before the video signal is read by the rotating head (s)

  tives so that the rotation and movement of the magnetic strip can be precisely controlled according to the synchronization information extracted from the signal.

  control returned by the fixed magnetic head.

  In most consumer video recorders using

  a strip 1.25 cm wide, the signal track

  strip occupies a width of 0.3 to 0.75 mm along the long edge

  tudinal of the strip so that this control signal is not

  not superimposed on the video and audio signal tracks. Therefore

  quent, the control signal may disappear due to an undesirable oscillation or displacement of the magnetic strip in the transverse direction. Because during the reproduction of the images, the control signal plays an important role in the precise positioning of the rotary head on

  recorded tracks, disappearance of this signal

  Mande results in poor quality of the reproduced images.

  In addition to the rotating magnetic head and the fixed magnetic head for recording and outputting the control signal, the conventional VCR includes a head

  and an audio head which are both fixed.

  The erase head is used to erase signals recorded prior to the new recording of video and audio signals and a control signal on a magnetic tape. The audio head is used to record and output the audio signals associated with the video signals. In particular, the conventional video recorder has three fixed magnetic heads in addition to the rotating magnetic head. These three fixed magnetic heads are arranged in the vicinity of the

  rotating head drum and therefore the structure

  turn of the rotary head drum is complicated.

  The present invention has been developed to eliminate the above-mentioned disadvantages and disadvantages

  conventional VCRs with one or more rotating heads

  tives of the helical scan type.

  Therefore, an object of the present invention is to obtain a method and an apparatus for recording and restoring

  a control signal on and from a recording tape

  magnetic in a video recorder where the control signal is recorded on all or almost all of the

  width of the magnetic strip so that the signal

  mande cannot suddenly disappear, thanks to which we obtain a precise operation of restitution of information in

VCR.

  According to a characteristic of the present invention,

  before recording the video signal using the magnetic head

  rotating tick, the control signal is recorded on the magnetic strip by creating a wide track corresponding substantially to the transverse width of the strip. Because the signal from

  order is recorded deep in the tape, a super

  position of the video signal on the control signal does not result in an erasure of the latter, so that the recorded control signal can be read during the playback of the

images.

  According to another characteristic of the present invention, the control signal is recorded and reproduced using a fixed head which also functions as an erasure head. Therefore, it is not necessary to use an exclusive recording / playback head

  for the control signal, as in the case of the magnet

  classic toscope and therefore the structure around the rotating head drum can be simplified, while manufacturing costs can be reduced *

  According to another characteristic of the present invention

  tion, it can be used as a fixed head functioning both as a control signal recording head and as a head

  of erasure, a head of the double airgap type which makes it

erase is high.

  According to another characteristic of the present invention

  tion, the distance between the two air gaps is such that we can choose a head of the double air gap type so that the signals coming from these two air gaps are in phase when we scan the configuration or repetitive model saved

  beforehand, of the control signal.

  According to another characteristic of the present invention

  tion, the respective width of the two air gaps in such a head of the double air gap type may be different from each other so that synchronization can be obtained

  accurate from the control head output signal.

  According to the present invention, a method of recording and restoring a control signal on and

  from a magnetic recording tape in a magnetic

  toscope comprising at least one rotary head for recording

  ment and the reproduction of a video signal on and from said magnetic recording tape, this method consisting in recording said control signal by means of a fixed head on said magnetic recording head so that said signal order is recorded on all or almost all

  the entire width of said magnetic recording tape

  tick, this recording operation being executed before the recording of said video signal which will be superimposed on said

  previously recorded control signal.

  According to the present invention, an apparatus is also obtained for recording and reproducing a control signal on and from a magnetic recording tape in a video recorder comprising at least one rotating head for recording and reproducing a signal. video on and from

  said magnetic recording tape, this apparatus

  nant: a means for generating said control signal Drésen-

  both a predetermined repetition frequency and a head

  fixed magnetic to record said control signal

  from said means on said magnetic recording tape

  and to restore the previous recorded control signal-

  said fixed magnetic strip being placed so that said control signal is recorded before said video signal is recorded by said rotary head, said fixed magnetic head comprising at least one air gap extending in the transverse direction of said magnetic strip of such

  so that this air gap covers all or almost all of

  the width of said magnetic recording tape "

  The object and characteristics of this invention

  tion will appear more easily on reading the description

  given below with reference to the accompanying drawings in which: Figure 1 is a schematic top plan view of part of a conventional video recorder; Figure 2 is a drawing of a recording track on a magnetic recording tape recorded by the various magnetic heads of the conventional VCR of Figure 1; Figure 3 is a schematic top plan view of part of a VCR in which a first embodiment of the present invention is used; Figure 4 is a drawing of a recording track on a magnetic recording tape recorded by the various magnetic heads of the video recorder of Figure 3 Figure 5 is a schematic top plan view of part of a VCR in which a second embodiment of the present invention is used; fi [Pure 6 is a drawing of a recording track on a magnetic recording tape recorded by the various magnetic heads of the video recorder of FIG. 5 FIG. 7 is a perspective view of a fixed head which can be used in the second embodiment of Figure 5; Figure 8 is a perspective view of another

  fixed head which can be used in the second embodiment

  sation of Figure 5; Figures 9 and 9B are waveform diagrams useful for understanding the operation of the fixed head of Figure 8; and Figure 10 is a block diagram of the electrical circuit used for recording and outputting a control signal to and from a recording tape

  in the VCR in Figure 5.

  Before describing the embodiments of the pre-

  invention, we will describe to better understand the latter a conventional process and apparatus5 for recording

  a control signal on a magnetic recording tape.

  Figure 1 is a partial top plan view

  schematic of a classic VCR. A tape recording

  magnetic T is guided by rollers 1 and 2 so as to

  partially wind around an IID rotating drum

  heads, comprising two rotating magnetic tates Ilv. The direction of movement of the strip is indicated by an arrow X, while the direction of rotation of the iiD head-holding rotary drum is designated by an arrow Y. The reference lie designates an erasing head over the entire width, for erasing signals previously recorded on the T-band, and the references Ha, lic denote an audio signal recording / playback head and a control signal recording / playback head0 The erasure head links

  is arranged in such a way that it precedes the part in

  registered by the ilv rotary heads fixed to the drum

  heads 111. In recording mode, the erase head on ia tot.lîtdt; (the width is supplied by an erasing current at a frequency that is erased so as to erase the information previously recorded on the magnetic tape Te The audio head is used to record and reproduce the signals

  audio, while the Hc control head is used to

  record and restore a control signal which is necessary

  to precisely control the rotation of the drum

  IID heads and the displacement of the magnetic tape T. Figure 2 shows a drawing of recording on the magnetic tape T in the case where a magnetic recording

  is carried out by the video recorder of figure 1. The drawing dten-

  registration is a drawing seen from the side of the strip T o is the magnetic substance, and the references Ha, Ho, He and Hv in FIG. 2 correspond respectively to the audio head Ha, to the control head Hc, to the erasing head He over the entire width, and at the rotary heads Hv of FIG. 1. In FIG. 2, the region I of the magnetic strip

  T is a part in which information remains

  previously registered; region II is a part of which the previously recorded information has been erased by the erasing head He over the entire width; and region III is a part in which a new recording has been made by the rotary heads

  Ilv, the audio head lia and the control head lie.

  In the track design on the magnetic strip T in Figure 2, the control track, which is formed on the magnetic strip T by recording a control signal using the control head He, has a width from 0.3 to 0.75 mm or a width of the edges of the magnetic strip T, and this control track is independent of other tracks such as video and audio tracks. Because the control track is formed on one of the edges of the magnetic strip T and the width of this magnetic strip is relatively small, the control signal may disappear due to scratches present on the magnetic strip T and an oscillation or displacement of the magnetic strip T in its transverse direction. In addition, as described above, an exclusive control head is required in the conventional magnetiscope so that the narrow control track is formed on one of the edges of the magnetic strip T. Figures 3 and 5 show first and first respectively second embodiments of the present invention. In particular, Figures 3 and 5 are schematic partial top plan views of VCRs used to implement the present invention. Various elements of Figures 3 and 5 corresponding to those of Figures t are designated by

  same references. In Figures 3 and 5, the HD reference denotes

  signs a rotating head drum; the references t and 2 of the rollers; the reference T a magnetic strip; Hv references two rotating magnetic heads attached to the HD head rotating drum; and the reference Ha an audio head. On the

  figure 3, the reference Hca designates a fixed head which is available

  located at a point preceding a part in which a recording

  is done by the rotary heads Hv. The fixed magnetic head Hca is a recording / restoring head for a control signal so that the control signal can be recorded over the entire width of the magnetic strip T from which previously recorded information has been erased by the erase head Re

  arranged at a point preceding the position of the fixed head Hca.

  As is well known, a main information signal, such as a video signal, is recorded and output by the heads

  11v rotating magnets performing helical scanning.

  Figure 4 is a track drawing showing various tracks on the magnetic head T of Figure 3. The track drawing of Figure 4 is a drawing seen from the side of the strip T o is the magnetic substance and the various heads mentioned above, Ha, Hv, IRca and He are also shown for a better understanding of this track drawing. In FIG. 4, region I is a part in which information recorded previously remains;

  region II is part of which information

  previously saved have been deleted by the He

  cement over the entire width; region III is a part in which only the control signal has been recorded by the fixed head Hca; and region IV is a part in which a main information signal (for example a chrominance signal transformed into low frequency and a luminensce signal transformed into high frequency are combined by frequency division multiplexing) is recorded on the tape magnetic T on which the control signal has already been recorded. In particular, in region IV, the signal for

  main video signal overlap or overlap

pose each other.

  In the second embodiment of FIG. 5, a fixed magnetic head Hec is used in place of the erasing head He and the control head Hc. of the first embodiment of FIG. 3. In particular, the fixed magnetic head Hec functions both as an erasing head and

a control head.

  FIG. 6 shows a track drawing on the magnetic strip T of FIG. 5, and the track drawing of FIG. 6 differs from that of FIG. 4 in that the region II of the erased part of FIG. 4 does not the drawing of

  track of figure 6, because the erasing, on the one hand, and the

  recording of the control signal, on the other hand, are carried out simultaneously by the fixed head Hec. In particular, regions II and III of FIG. 6 correspond respectively to the

regions III and IV of figure 4.

  In the above embodiments of the figures

  3 and 5, although the audio signal is adapted to be recorded

  recorded via the Haqui audio head is independent

  hanging from the Hv rotary magnetic heads, on an exclusive sound or audio track, the audio signal can be recorded by the Hv rotary heads with the audio signal combined with the main information signal by frequency division multiplexing or multiplexing with division in tempso If the audio signal is recorded this way, the performance

  in the use of the magnetic strip T can be increased.

  The high frequency signal applied to the total width erasing head He shown in FIG. 3 or to the fixed head Hec of FIG. 5 to perform an erasing operation at a frequency of 70 KHz for example, and an amplitude such that previously recorded information

  on the magnetic strip T can be erased satisfactorily

  doing. On the other hand, the control signal, which must be applied to the fixed head Hca in FIG. 3 and to the fixed head Hec in FIG. 5, has a frequency range such as the frequency range of the control signal reproduced by the Hv rotating magnetic heads is outside the frequency range of the main information signal recorded and output by Hv rotating magnetic heads. The control signal is preferably a square wave so that precise synchronization can be obtained. However, an ideal square wave occupies a wide frequency range due to

  of the presence of the harmonics of the fundamental wave.

  If we consider the repetition frequency of a square wave of 30 Hz with its harmonics up to the seventh, the frequency ma xi ma 1 e t is 2 1 0 Hz. T his maximum frequency is increased during the restitution information by the rotating magnetic heads Hv, and the increased frequency must be lower than the lower limit of the main information signal to prevent interference

  of the control signal. You can get such a com-

  control by passing a conventional square wave signal through a low pass filter with a cutoff frequency

such as 100 to 200 Hz.

  Adjust the amplitude of the control signal current

  so that the residual magnetism caused by the recording

  The control signal does not impart any noticeable distortion to the main information signal recorded by the Hv rotating magnetic heads. Although it is preferable to use a square wave as the control signal, this control signal can be a sine wave or a wave similar to a sine wave. When using a sine wave, it is not necessary to take into account the harmonics and, therefore, the frequency of this sine wave can be chosen simply so that the frequency of the control signal reproduced by the rotating magnetic heads Hv is

  is outside the frequency range of the information signal

main office.

  The point described above will be described in more detail by taking an example. We will assume that the speed of movement of the magnetic strip T is 33 mm per second and that the linear speed of the rotating magnetic heads Hv

  is 5.8 meters per second. In this case, the com-

  previously recorded tape T is

  restored by the rotating magnetic heads Mv with a frequency

  quence of 5.8 / (33 x 10-3) times the initial frequency. In suppo-

  As long as the maximum initial frequency of the control signal is 200 Hz, the control signal is reproduced in the form of a signal of approximately 35 KHz by the rotary magnetic heads Hv. This frequency is very far from the frequency range

  of the main information signal reproduced by the magnetic heads

  Hv rotating ticks since the lower limit of the frequency range of the main information signal is

about 100KHz.

  The fixed head Hca in Figure 3, receiving the control signal described above records the control signal as indicated by the vertical lines "c" in region III

  of Figure 4 on the part of the magnetic strip T of the

  which previously recorded information has been erased by the full width erase head He, as indicated by region II. In particular, the control signal is recorded again over the whole or almost the entire width of the magnetic strip T. On the other hand, in the embodiment of FIG. 5, the fixed head Hec receiving the signal command erases the information previously recorded in region I of the magnetic strip T of the

  Figure 6 across its entire width and, simultaneously

  memory, records the control signal indicated by the lines

verticals "c" in region II.

  In either case of Figures 4 or 6, because the frequency of the control signal is low, the control signal is recorded not only on the surface of the magnetic substance layer of the magnetic tape T but

  also deep in this layer of magnetic substance.

  Therefore, when the recording tracks of the main information signal are formed by the rotating magnetic heads Hv on the magnetic tape T, although the control signal is partially erased on the surface

  of the magnetic substance layer by the erase function-

  Using an FM wave as part of the main information signal, the control signal remains in the deep part of the magnetic substance due to the residual magnetism which has been generated by the recording.

  of the control signal and which remains in this deep part.

  The recorded control signal, which remains in the deep part of the magnetic substance as residual magnetism despite the overlying recording of the signal

  main information, can therefore be read satisfactorily

  health when restoring images. In addition, since the control signal is recorded over the whole or almost the entire width of the magnetic strip T and because the previously recorded control signal is read by the fixed head Uca or Hec, this is effectively avoided the disappearance of the control signal even if there is an undesirable oscillation or displacement of the magnetic strip T in the transverse direction. As a result, the previously recorded control signal can be continuously reproduced in the form of a signal having sufficient amplitude, while the control signal reproduced by the rotary magnetic heads Hv does not interfere with the signal. main information since the frequency range

  of the control signal reproduced by the rotating magnetic heads

  tives HT is outside the signal frequency range

main information.

  The fixed magnetic head Hec used in the second embodiment of FIG. 5 can be of the type with a single air gap or with two air gaps. However, it is better

  to use as a fixed head Hec a double-head type

  iron, which has a high efficiency in the erasing operation, since this Hec head must function not only as a control signal recording head but also as an erasing head. In the case where such a head of the double-gap type is used as the fixed head Hec of FIG. 5, the distance or interval between the two gaps can have a particular relationship with respect to the recording wavelength of the control signal on the magnetic recording tape T so that the control signal

  previously recorded can be restored satisfactorily

using the Hec fixed head.

  We will describe this point with reference to Figure 7 which shows a schematic perspective view of the fixed head

  Hec can be used in the video recorder of figure 5.

  The Hec double-head fixed head has two air gaps

  parallel irons gl and g2 spaced by a distance "d", and the magnetic strip T has been represented by mixed lines to show the position relation existing between the fixed head Hec and the magnetic strip T. In general, in

  heads of the double air gap type, such as those shown

  felt in FIG. 7, there are two kinds of winding structures in one of these, the signal polarities restored from the gaps gl and g2 being equal to each other and in the other of these , the signal polarities restored

being opposed to each other.

  In a fixed magnetic head Hec of the kind men-

  tioned first, in which output signals of the same polarity are formed at the two air gaps gl and g2, the distance Id "between the two air gaps gl e. g2 can be established so that the following relationship is satisfied td = nV / fo Nn'l is a positive integer "YV is the speed of movement of the magnetic strip T; "f" is the repetition frequency of the signal

order to be registered.

  On the other hand, in a fixed magnetic head Hec of the kind mentioned last, in which output signals of opposite polarity are formed at the two gaps gl and g2, the distance between the two gaps gl and g2 can be established so that the following relationship be satisfied: d = (2n + 1) V / 2f o In "is a positive integer" V "is the speed of the magnetic strip T;" f "is the repetition frequency of the signal

order to be registered.

  When the above formulas are satisfied respectively, the magnetic fluxes at the two air gaps gl and g2

are in phase.

  The fixed head Hec of the double air gap shown in FIG. 7 operates as follows. Assuming that the magnetic strip T moves in the direction of the arrow X shown in FIG. 7, the air gap g2 first records the control signal on the magnetic strip T, then

  the stored control signal is erased through the air gap gl.

  At this time, the control signal is again recorded by the gl gap. In particular, a repetitive command signal design indicated by the vertical lines "c" in FIG. 6 is formed by the air gap gl which is located opposite the magnetic strip T after the air gap g2. The recorded control signal is read when the images are restored

  by the fixed head Hes with double air gap as follows.

  Interval g2 first reads the command signal received

  previously registered, then the other gl gap performs the same operation. As a result, the corresponding waveform

  at the air gap gl can be superimposed on the corresponding waveform

  laying at the air gap g2 because the air gap g2 scans a subsequent crest, such as one of the transverse lines "c" on the

  FIG. 6, at the moment when the air gap gl is scanning an anterior crest.

  In particular, when the distance between the two air gaps

  is chosen as indicated above, the respective read signals-

  ment by the two aforementioned air gaps are in phase.

  When the images are restored, the com-

  demand previously recorded by the gl air gap of the t8te

  fixed Hec is therefore read by the two air gaps gl and g2 at the same time.

  Consequently, a resulting output is obtained from the two air gaps gl and g2 at the output terminal of the fixed head Hec. Although such a resulting output signal from the Hec fixed head is not a problem if the distance "d" between

  the two parallel air gaps was chosen as described above

  above, in case the distance "d" does not satisfy one

  of the formulas mentioned above, the output signal results

  so much did an inaccuracy in the synchronization of the restored control signal. This results in two peaks in the waveform of the resulting output signal from the head.

fixed Hec.

  Figure 8 shows a modification to the Hec fixed head of Figure 7 to solve the above mentioned problem. The fixed head Hec in FIG. 8 has a wider air gap g2 'and a narrower air gap gl. In particular, the two air gaps have different widths or spaces in the longitudinal direction of the strip. We will assume that these gaps g2 and gl are spaced apart by a distance which does not satisfy the above. When the previously recorded signal is output by the magnetic head

  fixed Hec of figure 8, the output signal of this pre-

  feels a waveform such as that shown in Figure 9A. In FIG. 9A, the reference Pgl designates the positive and negative peaks corresponding to the narrower air gap gl, while the reference Pg2 designates the positive peaks and

  negative corresponding to the wider air gap g2. We understand

  dra that the positive peak Pgl has a greater amplitude than the positive peak Pg2. The output signal of the fixed head Hec is processed by an appropriate comparator or by a circuit of

  blocking having a given threshold SL indicated in FIG. 9A.

  As a result, the comparator or the blocking circuit between

  generate an output signal in the form of a pulse train such as that shown in Figure 9B. Since the threshold is established at a value greater than the positive peak Pg2 and at a value less than the positive peak Pgl, the output pulses are only emitted with the positive peaks Pgl. Therefore, the information of the control signal read

  through the air gap g2 'are eliminated. We see from what pre-

  yields that the Hec double-gap fixed heads shown in FIGS. 7 and 8 both function as a single-gap head when restoring the images and in connection with the reading operation of the recorded control signal

previously.

  As regards also the operation of recording the control signal carried out by the fixed head Hca in FIG. 3 or Hec in FIG. 5, the level or amplitude of the signal

  The order to be registered is preferably established.

  as high a value as possible unless magnetic saturation occurs, so that the previously recorded control signal is restored with sufficient amplitude. However, if the level of the recording signal is too high, this control signal recorded on the magnetic tape T results in the appearance of a distortion in some of the low frequency components of the signal, especially in the low frequency components of the signal. signal, included in the main information signal or video signal recorded and reproduced by the rotating magnetic heads Hv. For example, the signals in the region of the chrominance signal transformed into low frequency in the frequency order of about 630 KHz are affected. In the presence of such a distortion, an undesirable difference in the components of color tones and of noise may appear in the restored images. "This distortion results from the interference between the control signal and the main information signal all two recorded on the same part of the magnetic recording tape T. The frequency of repetition of interference or distortion is defined by the ratio between the relative speed of the fixed magnetic heads He or Hec and the relative speed of the rotating magnetic head Hv, because the control signal having a given waveform is recorded in a pattern such as that indicated by the transverse lines "c" in Figures 4 and 6, so that the wave of the control signal is recorded as the shape of a repetition in the longitudinal direction of movement of the magnetic strip T. By noting this fact, we can eliminate the interference that appears in the restored images and n taking the following actions. In particular, by implementing the present invention, the ratio between the relative speed of the fixed magnetic head He or Hec and the relative speed of the rotary magnetic head Hec is chosen so that the video signal

  is nested with the repetition frequency mentioned above

  above the interference signal, so that an integer multiple of half the frequency of the horizontal synchronization signal is equal to the repetition frequency of the control signal reproduced by the rotating magnetic heads Hv, Thanks to this arrangement, the interference appearing in the restored images does not persist because the phase of the signal of in-

  terference reverses with each horizontal scan line.

  If it is assumed that the repetition frequency of the control signal is 30 Hz, and that the sweeping form of the video signal meets the standard of the NTSC system, the nesting mentioned above can be obtained by choosing the relative speed Hv rotating magnetic heads so that it

  is equal to 262.5 times the relative speed of the magnetic head

fixed tick Hca or Hec.

  Although the above embodiments have been

  described about a VCR with two rotating heads

  tives Hv, it goes without saying that the present invention could be adapted to various video recorders comprising one, three or more than three rotary heads. Furthermore, although FIGS. 4 and 6 show the video signal tracks without protective bands between the adjacent video tracks, it goes without saying that the present invention could be adapted both to a system in which bands of protection are present. protection. and a system in which protective bands are absent. Such a video track system without protective tapes is

  described in Japanese patent application No. 52-48919 corres-

  according to French patent application 76 31190.

  In FIGS. 4 and 6, the control signal is shown as being recorded on the magnetic strip T over almost the entire width of the strip T with the exception of one

  marginal part on which the audio signal track is located.

  Therefore, in the embodiment of Figures 5 and 6, the previously recorded audio signal remains ineffective when the magnetic tape passes through the fixed magnetic head Hec

  during registration. To erase the recorded audio signal

  previously recorded so that the Ha audio head can record a new audio signal on the audio signal track, an exclusive erase head can be used which

erases only the audio track-

  The way of recording audio signals is not limited to the example illustrated and mentioned above. In particular, the audio signal can be recorded by the rotating magnetic heads Hv together with the video signal. By using such an audio signal recording technique, the fixed audio magnetic head Ha can be omitted from FIG. 4 or from the figure 6. In particular, no fixed head

  is only necessary on one side of the rotating drum

  HD heads. This simplifies the structure of the VCR and decreases

its cost price.

  We will now refer to FIG. 10 which shows a block diagram of an electrical circuit used for

  record and play back the control signal through

  diary of the fixed magnetic head Hec of the second embodiment

  sation of figure 5. In figure 10, the reference 3 designates

  an input terminal for receiving a composite video signal.

  This composite video signal is applied to a synchronization signal separation circuit SEP, a circuit in which the horizontal synchronization signal Ph and the vertical synchronization signal Pv are separated respectively from the

* video signal. The vertical synchronization signal Pv is applied

  than a monostable MM multivibrator so that this multi-

  monostable vibrator generates a square wave signal Pc (of which

  the waveform has also been shown) at its output.

  The repetition frequency of the square wave signal Pc

  is 30 Hz, and this Pc signal is applied to a pass filter

  low LPF comprising transistors Q1 and Q2, resistors and capacitors. An example of each value of resistors and capacitors is shown for this filter

  low pass LPF and the other circuits which will be described below

  after. Their cut-off frequency (-3dB) of the low-pass filter is 100KHzI The role of the low-pass filter is to remove from the square wave signal Pc the high frequency components, i.e. the harmonics of higher order of the fundamental frequency of 30 Hz. More precisely, since the cut-off frequency of the low-pass filter LPF is 10 Hz, harmonics higher than the third order are rejected by the low-pass filter LPF,

  which results in the emission of a rounded square wave.

  The output signal of the low-pass filter LPF is designated by Se and its waveform has also been shown. This output signal Se is applied, in order to be amplified, to an amplifier

  power PA comprising transistors Q3 to Q6, resistors

  tances and capacitors. The amplified output signal of the power amplifier PA appearing at an output terminal 4 is used as a control signal (also designated by Se), and this control signal Se is applied to a first winding terminal of the head fixed Hec. The amplifier

  power PA has a supply terminal 5 via the

  medium from which electrical energy is applied to

  PA power amplifier only when recording

  has been completed. Thanks to this arrangement, the signal of com-

  request is recorded by the Hec fixed magnetic head on the

  magnetic strip T when the device is operating in record mode

  registration. A second terminal of the winding of the fixed magnetic head Hec is arranged so as to receive a high frequency current Se used for the erasing operation, this high frequency current Se being generated by an oscillator OSCe. In the example illustrated, the frequency of the erasing current Se is

70 KHz.

  A capacitor Ce is mounted between the first terminal of

  the winding of the head Hec and the mass. The value of the condensa-

  This is chosen so that its impedance at the high frequency of the erasing current Se is substantially zero, but at the frequency of the control signal Se it is much

  higher than the impedance of the Hec fixed magnetic head.

  A switch SV comprising a movable contact V is used to earth the second terminal of the winding

  of the Hec head during the restitution of the images. More precise-

  ment, the SV switch has a fixed contact P connected to the second terminal mentioned above, while the movable contact is grounded. Since the second terminal of the winding is grounded during the reproduction of the images, the restored signal is effectively applied to a

  signal processing circuit which will be described below.

  On the other hand, during the recording, the switch SI is open so that the erasing current Se is applied to the fixed magnetic head Hec. The SI switch can be an r'n. semiconductor or relay switch During recording, the control signal Se from the power amplifier PA flows through the fixed magnetic head Hec and part of the secondary winding 6 of an output transformer of the oscillator OSCe to ground and, simultaneously, the erasing current Se coming from the oscillator OSCe flows through the fixed magnetic head Hec and the capacitor Ce to ground. As a result, the control signal and the erasing current both pass through the winding of the fixed magnetic head.

  Hec by overlapping each other.

  The OSCe oscillator includes transistors Q7 and Q8, resistors and capacitors. A supply terminal 8

  in energy is connected to the OSCe oscillator, and the energy applied

  that at terminal 8 is deleted when the images are restored. In particular, the oscillator OSCe does not generate the erasure current Se during the reproduction of the images *

  We will now describe the structure and the function-

  nement of the circuit of FIG. 10 in conjunction with an information restitution operation. The control signal previously recorded on the magnetic strip T (see FIGS. 5 and 6) is read by the fixed magnetic head Hec, and therefore a control signal restored Ser is generated at the terminals of the winding of the head Hec. The restored control signal Scr is applied to a preamplifier PrA comprising an integrated circuit OA which comprises two differential amplifiers, resistors

and capacitors.

  The output signal of the PrA preamplifier, whose waveform is designated by the reference Sert, is applied

  to a waveforming circuit WA comprising two transa

  sistors Q9 and Q10, resistors and a capacitor. The cir-

  WA wave shaping circuit comprises a blocking circuit which generates at its output terminal 7 an output signal Pcr of square wave, the wave form of which is represented. This square wave output signal Pcr is used as a control signal to control the rotation of the HD rotating head drum (see FIG. 5) and the movement of the magnetic strip T of

  the same way as in the classic VCR.

  In the case where the H # tec of the double air gap type mentioned above and represented in FIG. 8 is used, the threshold SL mentioned above and represented in FIG. 9 can be advantageously adjusted by modifying the voltage

  blocking. Alternatively, the preamplifier can be designed

  not only so that it simply amplifies its Scr input signal, it also functions as a

  a comparator with an appropriate reference voltage corresponding to

corresponding to the established SL threshold.

  From the above description, it can be seen that due to the fact

  that the control signal is recorded on the magnetic tape T over the whole or almost the entire width of this strip in the present inventory. in the conventional VCR due to a deviation of the magnetic tape in

  its transverse direction relative to the control head.

  Therefore, there is no need to perform fine adjustment for alignment of the control head with the control signal track. In addition, a single fixed head can function as a recording / playback head for the

  control signal and simultaneously as an erasing head

  ment in the second embodiment of Figures 5 and 6.

  In this case, the exclusive control head used in the conventional VCR is not necessary and, therefore,

  we can simplify the structure around the rotating drum

  HD heads and lower the cost price. In addition, one can use

  be a head k double air gap with a yield of erasing-

  high as fixed head Hec of the second embodiment by choosing the interval between the two air gaps or by giving the two air gaps a different width. Consequently, precise synchronization is obtained from the resulting output signal supplied by the head fHec of type k double air gap. It is understood that the above deseription has only been given for illustrative and nonlimiting purposes, and that variants or modifications can be made

  in the context of the present invention.

REVLNDICATIONS

  1, Method for recording and restoring a signal

  control on and from a magnetic recording tape

  that in a video recorder comprising at least one magnetic head

  as rotary for recording and reproducing a video signal on and from said magnetic recording tape, the above-mentioned method being characterized in that it comprises an operation of recording the control signal by means of a fixed head on said magnetic recording tape so that said control signal is recorded over all or almost the entire width of said magnetic recording tape, said recording operation being performed before recording of said video signal which

  is superimposed on said previously recorded control signal.

  2. Method according to claim 1, characterized in that said control signal to be recorded by said fixed head has a frequency range such that the frequency range of the control signal reproduced by said rotating magnetic head is outside the frequency range of said video signal to be recorded and output

by said rotary head.

  3. Method according to claim 2, characterized in that one obtains said control signal to be recorded by passing a square wave signal having

  a given repetition frequency through a pass filter

  low so as to eliminate harmonics of higher order the fundamental frequency corresponding to said frequency of

repeat given.

  4. Method according to claim 1, characterized by

  the fact that the amplitude of said control signal is chosen

  before Mrs. recorded in such a way as to result in the appearance of a residual magnetism having an intensity such as the signal

  video recorded by said rotary head and to be super

  placed on the previously recorded control signal is free

  distortion despite this overlap.

  5. Method according to claim 1, characterized in that it further comprises a superposition operation

  a high frequency erasure current at said signal

  must be recorded by said fixed head so that said fixed head functions not only as a recording / restoring head of control signal but also as an erasing head which at least erases the signals

  video and control previously recorded.

  6. Apparatus for recording and reproducing a control signal on a magnetic recording tape in a

  VCR with at least one rotating head for recording

  record and reproduce a video signal on and from said magnetic recording head, the aforementioned apparatus being characterized in that it comprises: (a) first means for generating said control signal having a predetermined repetition frequency ; and (b) a fixed magnetic head for recording said control signal from said first means on said magnetic recording tape and for reproducing the previously recorded control signal, said fixed magnetic tape being placed so that said control signal is recorded before said video signal is recorded by said rotary head, said fixed magnetic head comprising at least one air gap extending in the transverse direction of said magnetic strip so that said air gap covers - all or almost the entire width of said

Magnetic recording channel.

  7. Apparatus according to claim 6, characterized in that it further comprises a second means for generating an erasure current and a third means for superimposing said erasure current on said control signal so that a superimposed signal is applied to the winding of said

  fixed head when recording.

  8O Apparatus according to claim 6, characterized in that said fixed head comprises two parallel air gaps so that the efficiency of erasure is high when

  this head functions as an erasure head.

  9. Apparatus according to claim 8, characterized in that the distance "d" between the two air gaps is chosen so that the signals read respectively by the two aforementioned air gaps are in phase when said fixed head scans

  the repetitive drawing of the previous recorded control signal-

  mento 10. Apparatus according to claim 9, characterized in that said distance "d" between the two air gaps is chosen so as to satisfy the following equation when the fixed head with double air gap is of the type generating output signals of the same polarity: d = n / fo "n" is a positive integer "V" is the speed of movement of said magnetic recording tape T; "f" is the repetition frequency of said signal

order to be registered.

  11. Apparatus according to claim 9, characterized in that said distance "'d" between the two air gaps is chosen so as to satisfy the following equation when the fixed head with double air gap is of the type generating polarity output signals opposite: d = (2n + 1) V / 2f where "n" is a positive integer "Vu is the speed of movement of said magnetic recording tape T;" f "is the repetition frequency of the signal

order to be registered.

  12. Apparatus according to claim 8, characterized in that the width of one of the air gaps is greater than the

  width of the other air gap so that the signals read respec-

  by the two air gaps have different amplitudes.

  13. Apparatus according to claim 12, characterized in that it further comprises a means for distinguishing from one another said signals read by the two aforementioned air gaps. 14. Apparatus according to claim 13, characterized in that the distinguishing means comprises a blocking circuit sensitive to the output signal of said fixed head *